Multi-cavity resonant circuits



p 9, 1958 A. DUBOIS MULTI-CAVITY RESONANT CIRCUITS Filed June 5. 1952 INVENTOR. ANDRE 0050/5 ATTORNEY United States Patent 2,851,633 MULTI-CAVITY RESONANT CIRCUITS Andr Dubois, Paris, France, assignor to Compagnie generale de Telegraphic Sans Fil, a corporation of rance This invention relates to cavity resonator magnetrons such as those used for ultra-high frequency generation or amplification, and more particularly to such magnetrons wherein plunger devices are provided the position of which in the cavities is adjustable to permit variation of the resonance frequency.

The main object of the invention is to widen the band of frequencies over which tubes having such multi-cavity resonators with plunger adjustment will operate and also to increase the outputs of such tubes.

According to the invention a magnetron tube comprising, within a vacuum tight enclosure, a cathode, an anode block having a plurality of cavity resonators, a cylindrical plunger penetrating axially into hollows formed in the anode segments and the position of which is adjustable to permit variation of the frequency of resonance of the cavities is characterised in that said plunger is provided with slots which extend across and thereby interrupt the paths of circulating currents which would otherwise be set up by induction when the tube 1s in operation.

The slots are preferably arranged in prolongation of the planes of symmetry of the anode segments of the tube and their number is preferably so chosen that the tube retains symmetry of revolution.

The invention is illustrated in and explained in connection with the accompanying drawings in which:

Figure 1 is a schematic view, partly in section and partly broken away, of a known magnetron tube of the multicavity resonator type with plunger adjustment for frequency and Figures 2 and 3 are mutually perpendicular views of the plunger of a tube in accordance with this invention and which, except for the said plunger, is as shown in Figure 1;

Figure 4 is a fragmentary view taken on line 4-4 of Figure 1 with part of the anode block and straps cut away.

Referring to Figure 1, the cavity magnetron therein represented has an axial cathode K, radial anode segments D and D defining cavities C and C, so-called straps a, b, a, b provided between the anodes to cause the tube, in a well known manner, to work in a desired mode and a circular tuning member or plunger P the position of which may be adjusted axially by means of a screw adjustment device V.

In such a magnetron as at present known the plunger P is a metal plate with concentric circular slots R, having the tube axis as centre, formed in its face as shown. As is known, the frequency of operation of the tube may be varied by adjusting the plunger axially to cause the annular protuberances S at the boundaries of the slots R of the plunger P to penetrate to a greater or lesser extent into the spaces adjacent to the straps.

When this tube is in operation the plunger is surrounded by a magnetic field which varies in value according to the value of the high frequency field produced, on the one hand, by the cavities the magnetic field of which reverses at each half-period, and on the other hand by the straps, which in fact carry varying currents. Accordingly induced currents are set up in the plunger and these represent energy loss.

In order to reduce these currents, the invention provides for radial slots or notches in the plunger plate to interrupt the paths for the induced currents. Such slots or notches are indicated at F in Figures 2 and 3, and cross the circular slots R at right angles. It should be pointed out that the scale adopted for Figure 1 is not quite the same as that for Figures 2 and 3.

Tests carried out by the applicant have shown that the invention enables the width of the band over which a multi-cavity magnetron can be tuned to be increased very considerably by way of example in one case the width rose from 10% to 20% of the mean frequency, and, for a given wavelength, the output increases, especially at wavelengths at which the plunger penetrates deeply between the straps. An increase in output has actually been obtained experimentally which is from 0.5 to 0.8.

I claim:

1. In a multicavity tunable magnetron of the type including a plurality of cavity resonators, strapping means and a movable circular tuning member, said circular tuning member comprising: a fiat portion perpendicular to the axis of the magnetron, said portion including circular grooves substantially co-extensive with and positioned to receive said strapping means upon movement of said member toward said strapping means, the improvement which comprises the provision of a plurality of radial slots in said flat portion regularly spaced around the axis thereof.

2. In a multicavity tunable magnetron of the type including a plurality of cavity resonators defined by anode segments in spaced apart relationship, strapping means and a movable circular tuning member, said circular tuning member comprising: a flat portion perpendicular to the axis of the magnetron, said portion including circular grooves substantially co-extensive with said strapping means and positioned for the latter to engage therein upon movement toward each other when the magnetron is tuned, the improvement which comprises the provision of a plurality of radial slots in said fiat portion regularly spaced around the axis thereof, the number of said radial slots being equal to the number of said anode segments, and their respective directions being perpendicular to said grooves and the same as the respective directions of said anode segments.

References Cited in the file of this patent UNITED STATES PATENTS 2,408,237 Spencer Sept. 24, 1946 2,422,465 Bondley June 17, 1947 2,448,573 Blazier et al. Sept. 7, 1948 2,481,171 Spencer Sept. 6, 1949 2,506,955 Fracassi May 9, 1950 2,509,419 Brown May 30, 1950 2,529,950 Kather Nov. 14, 1950 2,534,503 Donal, et al Dec. 19, 1950 2,589,903, Vitter Mar. 18, 1952 2,735,959 Kather Feb. 21, 1956 

